Typically, granular detergents are made via conventional spray drying techniques which produce spray dried granules having acceptable solubility in the laundering solutions. The acceptable solubility of the spray dried granules is primarily attributed to their high porosity, a feature which is grossly diminished when they are subjected to further processing such as agglomeration, grinding and/or pulverizing. Recently, there has been considerable interest within the detergent industry for laundry detergents which are "compact" and therefore, have low dosage volumes. The low dosage detergents are currently in high demand as they conserve resources and can be sold in small packages which are more convenient for consumers. In that regard, additional processing steps such as grinding and the like have been used to convert the porous spray dried granules into more "compact" granules. However, the resulting "compact" granules commonly do not possess favorable solubility characteristics, especially in low temperature washing solutions. Thus, it would be desirable to have a process which produces a detergent composition having improved solubility in the laundering solution.
More recent process developments relating to compact detergents have been directed to agglomeration techniques. For example, Curtis, European patent application No. 451,894 (Unilever), discloses a process for preparing high density detergent granules by using two mixers in series. In particular, an admix of starting detergent materials are fed into a high speed mixer/densifier after which the materials are fed into a moderate speed mixer/densifier to increase the bulk density further. Thus, Curtis initially requires a high speed mixer/densifier to pulverize the detergent granules and then a second moderate speed mixer/densifier to increase the density to the desired level.
The Curtis process, however, does not produce detergent agglomerates having satisfactory solubility in the laundering solution. The lower solubility characteristics are attributed, in part, to the relatively high levels of anionic surfactants typically contained in the so-called compact or low dosage detergents. Furthermore, compact detergent compositions having high levels of anionics tend to form a sticky gel phase upon contact with the laundering solution, a feature which exacerbates the solubility problem. It would therefore be desirable to have a process which produces a compact or high density detergent composition containing high levels of anionic surfactants and yet, maintains effective solubility in the laundering solution.
Accordingly, despite the aforementioned disclosures in the art, there is a need for a process which produces a high density detergent composition having a high level of anionic surfactant and exhibiting improved solubility in the laundering solution.